JP4911907B2 - Piezoelectric actuator and liquid ejection device - Google Patents

Description

The present invention relates to a piezoelectric actuator and a liquid ejection device, for example, a fuel injection injector, an inkjet printer, or a piezoelectric resonator, an oscillator, an ultrasonic motor, an ultrasonic vibrator, a filter or an acceleration sensor, a knocking sensor, an AE sensor, and the like. In particular, the present invention relates to a piezoelectric actuator and a liquid ejecting apparatus that are preferably used as a print head using spread vibration, elongation vibration, and thickness vibration.

  Conventionally, products using a piezoelectric ceramic include, for example, a piezoelectric actuator, a filter, a piezoelectric resonator (hereinafter, a concept including an oscillator), an ultrasonic vibrator, an ultrasonic motor, a piezoelectric sensor, and the like.

  Among these, for example, the piezoelectric actuator has a very high response speed to an electric signal on the order of μsec, so that it can be used as a piezoelectric actuator for positioning an XY stage of a semiconductor manufacturing apparatus, a piezoelectric actuator used for a print head of an inkjet printer, or the like. Applied. In particular, due to the recent increase in speed and price of color printers, there is an increasing demand for use in piezoelectric actuators for ink ejection such as inkjet printers.

  A piezoelectric element is used for such a piezoelectric actuator. For example, a ceramic substrate that acts as a ceramic diaphragm, and a first electrode layer, a piezoelectric layer, and a second electrode layer are provided on the ceramic substrate in this order. A so-called unimorph type piezoelectric actuator has been proposed (see, for example, Patent Document 1).

The ceramic substrate used as a ceramic diaphragm of such a piezoelectric actuator is made of zirconium oxide, aluminum oxide, magnesium oxide, aluminum nitride, silicon nitride, etc., but a displacement element is used on such a ceramic diaphragm. When bonding using an adhesive that cures at a high temperature of 100 ° C. or higher, the linear thermal expansion coefficients of the ceramic substrate and the displacement element are different, so that compressive stress is generated in the displacement element. There has been a problem that the piezoelectric characteristics of the displacement element are significantly lowered by the compressive stress. In order to solve this, it has been proposed that a ceramic substrate used as a ceramic diaphragm is composed of a piezoelectric material having the same composition (Patent Document 2).
International Publication No. 02/073710 Pamphlet JP 2004-165650 A

  However, although the piezoelectric actuator described in Patent Document 2 has an advantage of reducing the compressive stress, there is a problem that when the driving is repeated, the displacement is deteriorated, and as a result, the liquid discharge becomes unstable. .

Accordingly, an object of the present invention is to provide a piezoelectric actuator and a liquid ejection device that are excellent in driving durability.

The piezoelectric actuator of the present invention includes a plurality of displacement elements each having a piezoelectric layer made of a second piezoelectric ceramic sandwiched between a common electrode and a drive electrode on the surface of a ceramic diaphragm made of a first piezoelectric ceramic. The first piezoelectric ceramic and the second piezoelectric ceramic are either lead titanate, barium titanate, or lead zirconate titanate compounds, and the piezoelectric characteristics of d ₃₁ of the first piezoelectric ceramic are as follows. It is lower than the second piezoelectric ceramic.

In particular, piezoelectric properties d ₃₁ of the first piezoelectric ceramic is preferably 75% or less of the piezoelectric properties d ₃₁ of the second piezoelectric ceramic.

The first piezoelectric ceramics and a second piezoelectric ceramic, and wherein the containing Pb, Zr, Ti as the main component.

The lattice constant ratio of the first pressure Dense La Mix _c 1 / _{a 1} is from 1.013 to 1.030, the lattice constant ratio _c 2 / _{a 2} of said second piezoelectric ceramic is 1.01 to 1.016 And the value of c ₂ / a ₂ is smaller than the value of c ₁ / a ₁ .

The Zr / Ti ratio of the first pressure Dense La mix .96-.81, Zr / Ti ratio of said second piezoelectric ceramic is 1.17 to 0.92, and said first piezoelectric The Zr / Ti ratio of the ceramic is smaller than the Zr / Ti ratio of the second piezoelectric ceramic.

The liquid discharge apparatus of the present invention, the above-described piezoelectric actuator, it was joined with liquids pressurizing chamber, the flow path member having a nozzle hole communicating with the liquid pressure chamber, the liquid pressure The liquid filled in the chamber is pressurized by the piezoelectric actuator, and droplets are ejected from the nozzle holes.

  In order to obtain high displacement characteristics, it is indispensable to use the domain rotational strain of the piezoelectric body. In order to obtain such a large domain rotational strain, it is effective to use a rhombohedral composition near the MPB, or to add a trivalent or pentavalent or higher donor component.

  However, such a piezoelectric material having a large domain rotational strain is likely to change in crystal orientation due to stress. Therefore, if a substrate having the same composition as the piezoelectric material is used as a ceramic diaphragm, and the displacement is repeated, On the other hand, when stress is applied, the orientation state of the crystal changes. As a result, the inventors have found that the displacement deteriorates when the restraint state of the piezoelectric element changes.

Furthermore, in order to reduce the thermal stress due to the difference in coefficient of thermal expansion when performing simultaneous firing of the piezoelectric body and the electrode, the ceramic diaphragm is preferably a piezoelectric body of the same composition, but the displacement and durability In order to achieve both, the second piezoelectric ceramic to be displaced is a piezoelectric body with many domain rotation components , that is, a piezoelectric body with high piezoelectric characteristics , and the first piezoelectric ceramic is for suppressing crystal orientation. It was found that it is important to make a piezoelectric body with little domain rotation , that is, a piezoelectric body with low piezoelectric characteristics .

In this way, the first piezoelectric ceramic and the second piezoelectric ceramic are either lead titanate, barium titanate, or lead zirconate titanate compounds, and the piezoelectric characteristics of d ₃₁ of the first piezoelectric ceramic are expressed as follows. By making it lower than 2 piezoelectric ceramics, it is possible to realize a piezoelectric actuator and a liquid ejection device that are excellent in driving durability.

  The present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a piezoelectric actuator according to an embodiment of the present invention.

In FIG. 1, the piezoelectric actuator is provided with a plurality of displacement elements 7 on the surface of the ceramic diaphragm 2. Each displacement element 7, the common electrode 4, the piezoelectric layer 5 and the drive electrodes 6 are laminated in this order, are arranged piezoelectric layer 5 so as to sandwich the driving electrodes 6 and the common electrode 4. The common electrode 4 is grounded, and a voltage is applied to each drive electrode 6 from the outside. The piezoelectric layer 5 can be displaced by the voltage applied between the common electrode 4 and the drive electrode 6. Each displacement element 7 and the ceramic diaphragm 2 constitute a piezoelectric element 9.

According to the present invention, the ceramic diaphragm 2 is made of the first piezoelectric ceramic, the piezoelectric layer 5 is made of the second piezoelectric ceramic, and the first piezoelectric ceramic and the second piezoelectric ceramic are lead titanate. Or it is important that it is either a barium titanate or a lead zirconate titanate compound and is made of a material having a lower piezoelectric property of d ₃₁ of the first piezoelectric ceramic than that of the second piezoelectric ceramic. In this way, the first piezoelectric ceramic and the second piezoelectric ceramic are either lead titanate, barium titanate, or lead zirconate titanate compounds, and the piezoelectric characteristics of d ₃₁ of the first piezoelectric ceramic are expressed as follows. By making it lower than 2 piezoelectric ceramics, it is possible to realize a piezoelectric actuator and a liquid ejection device that are excellent in driving durability.

The pressure Dense la mix in the present invention means a ceramic that shows piezoelectricity, Bi layered compound and a tungsten bronze structure material, perovskite structure compounds of Nb alkali compounds, lead zirconate titanate containing Pb (PZT) And perovskite structure compounds containing lead titanate and the like, but among these, lead zirconate titanate and lead titanate containing Pb are suitable in terms of increasing wettability with the electrode and increasing adhesion strength with the electrode. It is.

  In particular, lead titanate and barium titanate are effective in obtaining a high binding force. That is, it is a crystal containing Pb as an A site constituent element and Zr and / or Ti as a B site constituent element. In particular, a lead zirconate titanate-based compound has a higher d constant. It is preferable for obtaining a piezoelectric sintered body having a large displacement.

The first piezoelectric ceramic and the second piezoelectric ceramic are either lead titanate, barium titanate, or lead zirconate titanate compound, and the piezoelectric characteristics of d ₃₁ of the first piezoelectric ceramic are expressed as the second piezoelectric ceramic. The lowering can be achieved, for example, by making the main components of both the same in order to reduce the difference in thermal expansion coefficient and changing the additive to change the piezoelectric characteristics. As a result, the second piezoelectric ceramic can be a piezoelectric body having many domain rotation components.

Specifically, PZT is used for the first piezoelectric ceramic, and at least one of Sr, Ba, Ni, Sb, Nb, Zn, Yb, and Te with respect to PZT as the main component for the second piezoelectric ceramic. By adding seeds, a more stable piezoelectric sintered body can be obtained. For example, what is formed by dissolving Pb (Zn _1/3 Sb _2/3 ) O ₃ and Pb (Ni _1/2 Te _1/2 ) O ₃ as subcomponents can be exemplified.

  In particular, it is desirable to further contain an alkaline earth element as the A site constituent element. As the alkaline earth element, Ba and Sr are particularly preferable in that a high displacement can be obtained, and the inclusion of 0.02 to 0.08 mol of Ba and 0.02 to 0.12 mol of Sr is particularly mainly tetragonal composition. It is advantageous to obtain a large displacement in the case of the following composition.

For _{example, Pb 1-x-y Sr} x Ba y (Zn 1/3 Sb 2/3) a (Ni 1/2 Te 1/2) b Zr 1-a-b-c Ti c O 3 + αwt% Pb 1 _{/ 2} NbO ₃ (0 ≦ x ≦ 0.14, 0 ≦ y ≦ 0.14, 0.05 ≦ a ≦ 0.1, 0.002 ≦ b ≦ 0.01, 0.44 ≦ c ≦ 0.50 , in which you express by alpha = 0.1 to 1.0).

Further, Zr / Ti ratio of the second piezoelectric ceramic 1.17-0.92, Zr / Ti ratio of the first pressure Dense La mix 0.96 to 0.81, and the first piezoelectric ceramic The Zr / Ti ratio is preferably smaller than the Zr / Ti ratio of the second piezoelectric ceramic in terms of obtaining a large restraining force.

Moreover, the lattice constant ratio _c 2 / _{a 2} of the second piezoelectric ceramic from 1.01 to 1.016, preferably from 1.011 to 1.013, the lattice constant ratio of the first pressure Dense La Mix _c 1 / a ₁ is from 1.013 to 1.030, preferably in that 1.015 to 1.017 are aligned and the thermal expansion the piezoelectric layer.

The piezoelectric property of d ₃₁ of the first piezoelectric ceramic is preferably 75% or less, particularly 70% or less of the piezoelectric property of d ₃₁ of the second piezoelectric ceramic. A low piezoelectric property means that the domain rotation is small, and the piezoelectric ceramic has a higher binding force.

  In addition, according to the present invention, since the common electrode 4 is manufactured by simultaneous firing, the common electrode 4 is made of a silver-palladium alloy containing 87% by volume or more, particularly 90% by volume or more, and further 93% by volume or more of silver. It is preferable to control the residual stress generated in the actuator 1 to 100 MPa or less. Thus, the effect which reduces the compressive stress by shrinkage | contraction of an electrode can be anticipated by making the silver component of the common electrode 4 into 87 volume% or more.

Further, in order to suppress aggregation of the common electrode 4, the average particle diameter of the common electrode 4 is preferably 0.1 to 5.0 μm. Further, the adhesion strength is increased, the residual stress is reduced, and the piezoelectric characteristic d ₃₁ is improved. order to further stabilize, at least a portion of the common electrode 4, particularly preferably the common electrode 4 comprises a pressure Dense la mix. The pressure Dense la mix 10-60 vol% when the total amount of silver-palladium alloy is 100% by volume, in particular 18 to 50 vol%, and more that are included in a proportion of 20 to 30 vol%, the common electrode This is good for reducing the residual stress while increasing the adhesion strength between the piezoelectric layer 4 and the piezoelectric layer 5.

Furthermore, the pressure Dense la mix for homogenization of residual stresses, it is preferable that the average crystal grain size of 0.3 to 1.0 [mu] m. Furthermore, 0.4 to 0.6 μm is preferable for suppressing defects. When the crystal grain diameter is controlled in this way, even when residual stress is generated, the residual stress generated in the plurality of displacement elements 7 is made uniform and the variation is small, so the influence on the piezoelectric characteristic d ₃₁ is small. Become.

  Next, the case where PZT is used as the piezoelectric ceramic will be described as an example of the method for manufacturing the laminated piezoelectric material of the present invention.

  First, as a raw material, a PZT powder is prepared as a first piezoelectric ceramic powder, and one of the above-described PZT materials is prepared as a second piezoelectric ceramic powder.

With the addition of suitable organic binders to these piezoelectric ceramic Powder was formed into tape-like, respectively, by applying the Ag-Pd paste was deposited as an internal electrode in a part of the green sheets formed, further, 10 to 50 MPa And then cut into a desired shape. This is debindered at about 400 ° C. and then fired. After firing, a desired electrode is formed on the surface and polarized to form a laminated piezoelectric body.

It is preferable raw density before sintering is 4.5 g / cm ² or more, by increasing the sintered density 4.5 g / cm ² or more, more can be fired at a low temperature, still raw Increasing the density also makes it easier to suppress evaporation of Pb.

  As shown in FIG. 2, the liquid ejection apparatus of the present invention is joined to a flow path member 13 having a liquid pressurizing chamber 13a and a nozzle hole 18 communicating with the liquid pressurizing chamber 13a. The liquid filled in the liquid pressurizing chamber 13a is pressurized by the piezoelectric actuator 11 and the liquid droplets are ejected from the nozzle hole 18 as an ink jet print head used in a recording apparatus using an ink jet system. It can be used suitably.

In the piezoelectric actuator 11, the common electrode 14 and the piezoelectric layer 15 are formed in this order on the ceramic diaphragm 12, and a plurality of drive electrodes 16 are formed on the surface of the piezoelectric layer 15. A plurality of displacement elements 17 having a structure sandwiched between the common electrode 14 and the drive electrode 16 are formed on the ceramic diaphragm 12.

The piezoelectric actuator 11, a plurality of grooves are provided in parallel, formed by bonding the flow path member 13 having a partition wall 1 3b for partitioning the liquid pressurizing chamber 1 3 a and each groove is a groove. Junction is ceramic diaphragm 12 is joined by using an adhesive or the like to the flow path member 13 so as to space and contact the liquid pressurizing chamber 13a, each of the drive electrodes 16 of the displacement element 17 is a liquid under pressure It is provided so as to be disposed immediately above the chamber 13a. Each displacement element 17 and the ceramic diaphragm 12 constitute a piezoelectric element 19.

Then, applying a voltage from the drive circuit between the common electrode 14 and the driving electrode 16, the ink pressurized in the liquid pressurizing chamber 13a corresponding to the displacement element 17 to which a voltage has been applied displacement, the piezoelectric element 1 9 By oscillating, the ink in the liquid pressurizing chamber 13 a is pressurized, and ink droplets are ejected from the nozzle holes 18 opened in the bottom surface of the flow path member 13.

  By using the laminated piezoelectric material of the present invention as the piezoelectric actuator of such a print head, a print head can be realized using an inexpensive IC.

  Since the print head of the present invention is excellent in displacement characteristics, a feature of high-speed and high-precision ejection is obtained, and a print head suitable for high-speed printing can be provided. In addition, by mounting the print head of the present invention on a printer, for example, a printer including an ink tank that supplies ink to the print head and a recording paper transport mechanism for printing on a recording paper is conventionally provided. Compared to, high-speed and high-precision printing can be easily achieved.

  The laminated piezoelectric material of the present invention was produced and applied to an ink jet print head as a piezoelectric actuator.

First, as a raw material, it was prepared piezoelectric ceramic Powder containing 99% or more of lead zirconate titanate.

  The green sheet is made by adding butyl methacrylate as an aqueous binder, polycarboxylate ammonium salt as a dispersant, isopropyl alcohol and pure water as a solvent to a piezoelectric ceramic powder mainly composed of lead zirconate titanate. After mixing, this slurry was prepared in the form of a sheet having a thickness of 30 μm on a carrier film by the doctor blade method.

Green sheets having two compositions for piezoelectric layers and ceramic diaphragms shown in Table 1 were prepared and combined.

Further, the internal electrode paste was printed at a thickness of 4 μm on the surface of the ceramic diaphragm green sheet to form the internal electrode.
Furthermore, the green sheet for piezoelectric layers was laminated on the ceramic diaphragm green sheet with the surface on which the internal electrodes were printed facing upward, and pressed to obtain a laminate.

After degreasing the laminated body, the laminated body is sintered by being held in an atmosphere of 980 ° C. and oxygen of 99% or more for 4 hours, and is composed of the piezoelectric layer 5 , the ceramic diaphragm 2, and the common electrode ( internal electrode ) 4. The body was made. A drive electrode 6 was formed on one side of the surface. The drive electrode 6 was coated with Au paste by screen printing. This was formed by baking at 600 to 800 ° C. in the air.

Finally, lead wires were connected to the drive electrodes 6 by soldering to complete a piezoelectric element 9 having a shape as shown in FIG.

Next, a displacement evaluation method for piezoelectric elements will be described. The piezoelectric element 9 having the shape shown in FIG. 1 was processed into a size of 8 mm × 8 mm, and this substrate was bonded to a metal substrate having a 10 mm × 10 mm outer shape with a 4 mm × 4 mm hole, to obtain a displacement measurement sample. In addition, we polarization by applying a DC voltage of 3k V / mm 5 minutes and the common electrode 4 in the thickness direction between the driving electrodes 6. Displacement under a voltage of 2 kV / mm was performed. The displacement was measured with a Doppler displacement meter. The displacement was measured after displacement for 50 hours, and the amount of deterioration of the displacement was determined. The results are shown in Table 1.

Sample No. of the present invention. 2-12, the displacement is Ru der than 53 nm, the displacement deterioration rate after the durability test of 50 hours is 5% or less.

  On the other hand, sample No. 1 outside the scope of the present invention in which the first piezoelectric ceramic and the second piezoelectric ceramic are the same. No. 1 had a large deterioration rate of 10% or more.

It is a schematic sectional drawing which shows the structure of the piezoelectric actuator of this invention. It is a schematic sectional drawing which shows the structure of the liquid discharge apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 ... Piezoelectric actuator 2, 12 ... Ceramic diaphragm 4, 14 ... Common electrode 5, 15 ... Piezoelectric layer 6, 16 ... Drive electrode 7, 17 ... Displacement element
9, 19 ... Piezoelectric element 13 ... Channel member 13a ... Liquid pressurizing chamber 13b ... Partition 18 ... Nozzle hole

Claims (6)

A plurality of displacement elements each having a piezoelectric layer made of a second piezoelectric ceramic sandwiched between a common electrode and a drive electrode are provided on the surface of a ceramic diaphragm made of the first piezoelectric ceramic. And the second piezoelectric ceramic is any one of lead titanate, barium titanate, or lead zirconate titanate compounds, and the piezoelectric characteristic of d ₃₁ of the first piezoelectric ceramic is higher than that of the second piezoelectric ceramic. A piezoelectric actuator characterized by being low. 2. The piezoelectric actuator according to claim 1, wherein the piezoelectric property of d ₃₁ of the first piezoelectric ceramic is 75% or less of the piezoelectric property of d ₃₁ of the second piezoelectric ceramic. 3.   The piezoelectric actuator according to claim 1 or 2, wherein the first piezoelectric ceramic and the second piezoelectric ceramic contain Pb, Zr, and Ti as components. The lattice constant ratio c ₁ / a _{1 of} the first piezoelectric ceramic is 1.013 to 1.030, the lattice constant ratio c ₂ / a _{2 of} the second piezoelectric ceramic is 1.01 to 1.016, and the piezoelectric actuator according to claim 1, the value of c ₂ / _{a 2} is equal to or smaller than the value of _{c 1} / _a 1.   The Zr / Ti ratio of the first piezoelectric ceramic is 0.96 to 0.81, the Zr / Ti ratio of the second piezoelectric ceramic is 1.17 to 0.92, and the Zr of the first piezoelectric ceramic is Zr / Ti. The piezoelectric actuator according to claim 1, wherein a / Ti ratio is smaller than a Zr / Ti ratio of the second piezoelectric ceramic.   The piezoelectric actuator according to any one of claims 1 to 5 is joined to a flow path member including a liquid pressurizing chamber and a nozzle hole communicating with the liquid pressurizing chamber. A liquid ejecting apparatus, wherein the filled liquid is pressurized by the piezoelectric actuator, and droplets are ejected from the nozzle holes.

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